Optimization of vacuum systems and methods for drying drill cuttings

ABSTRACT

Systems and methods for separating fluids from drill cuttings. Specifically, the invention relates to shakers that incorporate a vacuum system and methods of operating such systems to effect a high degree of fluid separation. The system and methods are effective across a variety of screen sizes, vacuum flows and vacuum designs.

FIELD OF THE INVENTION

The invention describes systems and methods for separating fluids fromdrill cuttings. Specifically, the invention relates to shakers thatincorporate a vacuum system and methods of operating such systems toeffect a high degree of fluid separation. The system and methods areeffective across a variety of screen sizes, vacuum flows and vacuumdesigns.

BACKGROUND OF THE INVENTION

The loss of drilling fluids presents several technological and costchallenges to the energy exploration industry. These challengesgenerally include the seepage losses of drilling fluids to theformation, the recovery of drilling fluids at surface and/or thedisposal of drilling detritus or cuttings that are contaminated withdrilling fluid. In the context of this description, “drilling fluid” isboth fluid prepared at surface used in an unaltered state for drillingas well as all fluids recovered from a well that may include variouscontaminants from the well including water and hydrocarbons.

As is known, and by way of background, during the excavation or drillingprocess, drilling fluid losses can reach levels approaching 300 cubicmeters of lost drilling fluid over the course of a drilling program.With some drilling fluids having values in excess of $1600 per cubicmeter, the loss of such volumes of fluids represents a substantial costto drill operators. Drilling fluids are generally characterized aseither “water-based” or “oil-based” drilling fluids that may includemany expensive and specialized chemicals as known to those skilled inthe art. As a result, it is desirable that minimal quantities ofdrilling fluids are lost during a drilling program with the result beingthat many technologies have been employed to minimize drilling fluidlosses both downhole and at surface. Additionally, in some areas thedelivery of oil or water for the formulation of drilling fluids canpresent several costly challenges for some operations; specificallydesert, offshore and even some districts where communities will notallow allocation of water for this use.

As noted above, one particular problem is the separation of drillingfluid and any hydrocarbons from the formation that may be adhered to thedrill cuttings (collectively “fluids”) at the surface. The effectiveseparation of various fluids from drill cuttings has been achieved byvarious technologies including but not limited to; hydrocyclones, mudcleaners, linear motion shakers, scroll centrifuges, vertical basketcentrifuges (VBC), vacuum devices, and vortex separators. As known tothose skilled in the art, these devices typically rent out at costsranging from $1000 to $2000 per day and, as a result, can represent asignificant cost to operators. Thus, the recovery of fluids necessary torecover these costs requires that the recovered fluid value is greaterthan the equipment rental cost in order for the recovery technology tobe economically justified. On excavation projects where large amounts ofhigh-cost drilling fluid are being lost (for example in excess of 3cubic meters per day), then daily rental charges for specializedseparation equipment can provide favorable economics. In addition, anoperator will likely also factor in the environmental effects and/orcosts of disposal of drilling fluid contaminated drill cuttings indesigning their drilling fluids/drill cutting separation/recoverysystems.

Further still, past techniques for separating drilling fluid from drillcuttings have also used liquid spraying systems to deliver “washing”liquids to drill cuttings as they are processed over shaker equipment.Such washing liquids and associated fluid supply systems are used todeliver various washing fluids as the cuttings are processed over ashaker and can include a wide variety of designs to deliver differentwashing fluids depending on the type of drilling fluid being processed.For example, washing liquids may be comprised of oil, water, or glycoldepending on the drilling fluid and drill cuttings being processed overthe shaker. Generally, these washing fluids are applied to reduce theviscosity and/or surface tension of the fluids adhered to the cuttingsand allow for more fluids to be recovered. However, these techniqueshave generally been unable to be cost effective for many drilling fluidsas the use of diluting fluids often produces unacceptable increases indrilling fluid volume and/or changes in chemical consistency and, hence,rheological properties of the drilling fluid.

Thus, while various separation systems are often effective and/orefficient in achieving a certain level of fluids/cuttings separations,each form of separation technology can generally only be efficientlyoperated within a certain range of conditions or parameters and atparticular price points. For example, standard shakers utilizing screensare relatively efficient and consistent in removing a certain amount ofdrilling fluid from cuttings where, during the typical operation of ashaker, an operator will generally be able to effect drillingfluid/cuttings separation to a level of 12-40% by weight of fluidsrelative to the drill cuttings (i.e. 12-40% of the total mass ofrecovered cuttings is drilling fluid). The range of fluids/cuttings wt %is generally controlled by screen size wherein an operator can effect ahigher degree of fluids/cuttings separation by using a larger screenopening (eg. 50-75 mesh) and a lower degree of fluids/cuttingsseparation with a smaller screen opening (eg. up to 325 mesh). Thetrade-off between using a large mesh screen vs. a small mesh screen isthe effect of mesh screen size on the quantity of solids passing throughthe screen. That is, while an operator may be able to lower the fluidsretained on cuttings coming off the shaker with a larger mesh screen(50-75 mesh), the problem with a larger mesh screen is thatsubstantially greater quantities of solids will pass through the screen,that then significantly affect the rheology and density of the recoveredfluids and/or require the use of an additional and potentially lessefficient separation technology to remove those solids from therecovered drilling fluids. Conversely, using a small mesh screen, whilepotentially minimizing the need for further downstream separationtechniques to remove solids from recovered drilling fluids, results insubstantially larger volumes of drilling fluids not being recovered, asthey are more likely to pass over the screens hence leading to increaseddrilling fluids losses and/or require subsequent processing.

Accordingly, in many operations an operator will condition fluidrecovered from a shaker to additional processing with a centrifugalforce type device in order to reduce the fluid density and remove asmuch of the fine solids as possible before re-cycling or re-claiming thedrilling fluid. However, such conditioning requires more expensiveequipment such as centrifuges, scrolling centrifuges, hydrocyclones,etc., which then contribute to the overall cost of recovery. Theseprocessing techniques are also directly affected by the quality of thefluid they are processing, so fluids pre-processed by shakers usingcoarse screen will not be as optimized as those received from finerscreens.

Furthermore, the performance of centrifuges and hydrocyclones and otherequipment are directly affected by the viscosity and density of the feedfluid. As a result, drilling fluid recovery techniques that send heavy,solids-laden fluids to secondary processing equipment require moreaggressive techniques such as increased g-forces and/or vacuum to effectseparation which will typically cause degradation in the drill cuttings.

Thus, the operator will try to balance the cost of drilling fluid losseswith the quality of the fluid that is recovered together with otherconsiderations. While operators will typically have little choice in thequality of the cuttings processing and fluid recovery techniquesavailable, many operators will operate separation equipment such thatthe recovered drilling fluid density from the separation equipment willbe about 200-300 kg/m³ heavier than the density of the circulating fluidin the system. This heavier fluid which would contain significantquantities of fine solids and that when left in the drilling fluid willeither immediately or over time impair the performance of the drillingfluid or any other type of fluid.

As a result, there continues to be a need for systems that economicallyincrease the volume of fluids recovered from a shaker without negativelyimpacting the rheological properties of the recovered drilling fluid.More specifically, there has been a need for separation systems thatresult in recovered fluid densities in the range of 5-100 kg/m³ relativeto the original fluid density and that do not affect rheologicalproperties such as plastic viscosity and gel strength.

In addition, there has been a need to develop a low-cost retrofittechnology that can enhance fluid recovery and do so at a fractionalcost level to mechanisms and technologies currently employed.

The use of vacuum technology has been one solution to improving theseparation of drilling fluids. However, vacuum technology in itselfpresents various problems including insufficient cuttings/fluidsseparation that, as noted above, requires additional and expensivedownstream processing, and its inability to effectively remove finesfrom the recovered drilling fluid which contributes to an increase inthe density of the recovered drilling fluid. Moreover, aggressive vacuumsystems will also degrade cuttings such that the problem of creatingfines is increased.

In addition, various vacuum technologies may also present dust and mistproblems in the workplace as, with past vacuum techniques, there is aneed to regularly clean clogged screens with high pressure washes. Highpressure washing of screens creates airborne dust and mist hazards tooperators. Thus, there continues to be a need for technologies thatminimize the requirement for screen washing.

Further still, there has been a need for improved fluid separationsystems on the underside of a vacuum screen that allows relatively largevolumes of air to be drawn through a vacuum screen to be effectively andefficiently separated from the relatively low volume of drilling fluidbeing drawn through a vacuum screen. That is, there has been a need forimproved fluid/air separation systems. There has also been a need forvacuum technologies that assist in the oxidation of fatty acids within adrilling fluid that may reduce the need for additional emulsifiers.

Operationally, there has also been a need for improved methods ofoperating a vacuum system that effectively minimizes the risk of screenclogging but that also enables the use of finer screens.

Further still, there has been a need for systems that allow for theefficient replacement of screens but that also provide improved gasketsand sealing between the vacuum system and the screens.

PRIOR ART REVIEW

A review of the prior art reveals that various technologies includingvacuum technologies have been used in the past for separating drillingfluids from drill cuttings including vibratory shakers.

For example, U.S. Pat. No. 4,350,591 describes a drilling mud cleaningapparatus having an inclined travelling belt screen and degassingapparatus including a hood and blower. U.S. Patent Publication No.2008/0078700 discloses a self-cleaning vibratory shaker having retro-fitspray nozzles for cleaning the screens. Canadian Patent Application No.2,664,173 describes a shaker with a pressure differential system thatapplies a non-continuous pressure across the screen and other prior artincluding U.S. Pat. Nos. 6,092,390, 6,170,580, U.S. Patent Publication2006/0113220 and PCT Publication No. 2005/054623 describe variousseparation technologies.

Thus, while past technologies may be effective to a certain degree inenabling drilling fluid/cuttings separation, the prior art is silent inaspects of the design and operation of separation devices that enablefluid removal to substantially improved levels. Specifically, the priorart is silent with respect to achieving fluids retained on cuttingslevel below about 12% by weight and that does not have an adverse effecton the density of recovered drilling fluid.

SUMMARY OF THE INVENTION

In accordance with the invention systems and methods for separatingdrilling fluid from drill cuttings improved vacuum systems aredescribed.

In a first embodiment, an apparatus for improving the separation ofdrilling fluid from drill cuttings on a shaker is provided, theapparatus comprising: a shaker screen having an upper side and a lowerside for supporting drilling fluid contaminated drill cuttings within ashaker; an air vacuum system operatively connected to a section of theshaker screen for pulling an effective volume of air through the sectionof the shaker screen to enhance the flow of drilling fluid through thesection of the shaker screen and the separation of drilling fluid fromdrill cuttings; and, a drilling fluid collection system for collectingthe separated drilling fluid from the underside of the screen and theair vacuum system; wherein the air vacuum system draws a volume of airthrough the screen that minimizes damage to the drill cuttings whileenhancing the amount of drilling fluid removed from the drill cuttingsand maintaining an effective flow of drill cuttings off the shaker.

In various embodiments, the invention provides additional functions andstructures.

In one embodiment, the air vacuum system includes: a vacuum manifold foroperative connection to a shaker and a section of the shaker screen; avacuum hose operatively connected to the vacuum manifold and a vacuumpump operatively connected to the vacuum hose.

In another embodiment, the invention further includes a fluid/gasseparation system operatively connected to the vacuum pump.

In another embodiment, the fluid/gas separation system is a multi-stagefluid separation system.

In another embodiment, the vacuum manifold has a funnel shaped portionfor operative connection to a vacuum hose.

In yet another embodiment, the vacuum manifold is positioned adjacentthe downstream end of the shaker screen.

In further embodiments, the vacuum manifold extends up to 75% of thetotal length of the shaker screen towards the upstream end, up to 33% ofthe total length of the shaker screen or up to 15% of the total lengthof the shaker screen. In one embodiment, the vacuum manifold is adaptedfor configuration to the shaker screen across 5-15% of the length of theshaker bed.

In yet further embodiments, the vacuum pump is adjustable to control thevacuum pressure and/or applies a pulsating vacuum pressure.

In another embodiment, the vacuum manifold includes a positioning systemfor altering the position of the vacuum manifold with respect to theshaker screen.

In yet another embodiment, the shaker screen includes a shaker frame andthe shaker frame and associated shaking members are manufactured fromcomposite materials.

In yet further embodiments, the shaker screen is 50-325 mesh or acombination thereof or 80-150 mesh or a combination thereof.

In one embodiment, the vacuum system pulls air through the screen at avelocity less than 8400 feet per minute.

In another embodiment, the air velocity through the screen is sufficientto produce a consistency in the drill cuttings exiting the shaker ofsemi-dry cement.

In another embodiment, the manifold includes a lip supporting a gasketand the screen operatively engages with the gasket and lip.

In further embodiments, the drilling fluids retained on cuttings is lessthan 12 wt %, less than 10 wt %, less than 8 wt % or less than 6 wt %.

In another embodiment, the system further comprises an air injectiondevice for operative injection of a compressed gas into the drillingfluid for foaming the drilling fluid prior to drilling fluid contactingthe shaker screen.

In another embodiment, the system further comprises a gas detectorwithin the vacuum system for measuring the quantity and/or compositionof gas released from the drilling fluid.

In another embodiment, the system further comprises at least one massmeasurement system operatively connected to the shaker for measuring therelative mass of drill cuttings and fluid on the shaker.

In one embodiment, the mass measurement system includes at least twosensors positioned at different locations on the shaker bed and adisplay system for outputting the relative mass on the shaker at thedifferent locations.

In another embodiment, the system further comprises a spargeroperatively connected to the shaker for injecting gas into the drillingfluid before the drilling fluid is delivered to the shaker screen.

In one embodiment, the air vacuum system is designed for retro-fitconnection to a shaker.

In another aspect, the invention provides a method of optimizing theperformance of a drill cuttings shaker comprising the steps of: a)introducing drill cuttings contaminated with drilling fluid to anupstream end of a shaker bed having a shaker screen; and b) applying avacuum force to the shaker screen sufficient to effectively reducedrilling fluid retained on cuttings to a level below that obtained whenno vacuum force is applied.

In another embodiment, the invention also provides the step ofrecovering drilling fluid from the underside of the shaker screen andwherein the plastic viscosity of the drilling fluid is substantiallyequivalent to the plastic viscosity of an original drilling fluid priorto introduction into a well.

In various aspects of the method, the drilling fluids retained oncuttings after step b is less than 12 wt %, less than 10 wt %, less than8 wt % or less than 6 wt %.

In another embodiments, the vacuum pressure is applied to up to 75% ofthe total length of the shaker screen, up to 33% of the total length ofthe shaker screen or to the downstream 5-15% of the shaker screen.

In another embodiment, the air flow is controlled to prevent stalling ofdrill cuttings on the screen.

In yet another embodiment, the air flow is sufficient to produce aconsistency in the drill cuttings exiting the shaker of semi-dry cement.

In further embodiments, the air flow is less than 8400 feet per minuteand/or the air flow is controlled to cause defoaming of a drillingfluid.

In one embodiment, the drilling fluid is foamed prior to contacting theshaker screen.

In one embodiment, the quantity and/or composition of gas recovered fromthe drilling fluid is measured within the vacuum system.

In yet another embodiment, the air flow through the vacuum screen iscontrolled to effect fatty acid oxidation within the drilling fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described by the following detailed description anddrawings wherein:

FIG. 1 is a perspective view of a bottom perspective view of a vacuumframe assembly and manifold in accordance with one embodiment of theinvention;

FIG. 1A is an exploded end view of a screen, vacuum frame assembly andmanifold in accordance with one embodiment of the invention;

FIG. 1B is a side view of a vacuum frame assembly and manifold inaccordance with one embodiment of the invention;

FIG. 1C is a top perspective of a vacuum frame assembly and manifold inaccordance with one embodiment of the invention;

FIG. 1D is a perspective view of a screen assembly in accordance withone embodiment of the invention;

FIG. 1E is a perspective bottom view of a vacuum frame assembly andscreen in accordance with one embodiment of the invention;

FIG. 2A is a side view of a shaker retrofit with the vacuum frameassembly and vacuum system in accordance with one embodiment of theinvention;

FIG. 2B is a side view of a shaker retrofit with the vacuum frameassembly and vacuum system in accordance with one embodiment of theinvention;

FIG. 3A is a top view of a shaker retro-fit with a screen and vacuumsystem in accordance with one embodiment of the invention;

FIG. 3B is a top view of a shaker retro-fit with a vacuum system inaccordance with one embodiment of the invention;

FIG. 3C is a front view of a shaker retro-fit with a screen and vacuumsystem in accordance with one embodiment of the invention;

FIG. 3D is a front view of a shaker for retro-fitting in accordance withone embodiment of the invention;

FIG. 4 is a plan view of typical shaker bed for retro-fit with a vacuumframe and manifold in accordance with one embodiment of the invention;

FIG. 5 is a plan view of typical shaker bed retro-fit with a vacuumframe and manifold showing vacuum conduits leading away from the shakerbed in accordance with one embodiment of the invention;

FIG. 6 is a plan view of typical shaker bed retro-fit with a vacuumframe and manifold and screen in accordance with one embodiment of theinvention;

FIG. 7 is a table showing a cost analysis of vacuum-processed drillingfluid as compared to a prior art processing method;

FIG. 8 is a graph showing drilling fluid parameters as a function ofwell depth for a drilling fluid subjected to a rotary vacuum separation;

FIG. 9 is a graph showing drilling fluid parameters as a function ofwell depth for a drilling fluid subjected to a rotary vacuum separation;

FIG. 10 is a graph showing drilling fluid parameters as a function ofwell depth for a drilling fluid subjected to a vacuum screen separationin accordance with one embodiment of the invention;

FIG. 11 is a graph showing drilling fluid parameters as a function ofwell depth for a drilling fluid subjected to a vacuum screen separationin accordance with one embodiment of the invention;

FIG. 12 is a schematic diagram of a further embodiment having a gasinjection system in accordance with one embodiment of the invention;and,

FIG. 13 is a graph comparing primary and secondary emulsifier usage inwells using roto-vac and vacuum screen technologies.

DETAILED DESCRIPTION

In accordance with the invention and with reference to the figures,embodiments of an improved drilling fluid recovery method and apparatusare described.

Importantly, the systems and methods described enhance the separation ofdrilling fluids and drill cuttings therein providing an improvement inthe removal or reduction of drilling fluids retained on cuttings values.In addition, the systems and methods can provide improved separationswithout significantly affecting the rheological properties of thedrilling fluid.

More specifically, the invention solves various technical problems ofprior approaches to cleaning drill cuttings and recovering drillingfluids at the surface during drilling operations, and particularlyproblems in conjunction with known shaker systems. In addition, theinvention describes methods of optimizing the separation of fluids fromdrill cuttings recovered at surface

For the purposes of illustration, FIGS. 2A-2B and FIG. 4 show a knownshaker 10 having a generally flat screen bed 12 comprised of multiplesections 20 over which recovered drilling fluid and drill cuttings arepassed. The shaker 10 typically includes a dual motor shaking system 14to impart mechanical shaking energy to the screen bed. Recovereddrilling fluid and cuttings from a well are introduced to the upstreamend of the screen bed 16 wherein the mixture of drilling fluid andcuttings move toward the downstream end 18 where the “dried” drillcuttings flow off the end of the shaker. The vibrating motion of theshaker and screen bed effects separation of the drill cuttings andfluids wherein the drilling fluid passes through the screen bed and isrecovered from the underside of the shaker 10 and drill cuttings arerecovered from the downstream end 18 of the screen bed. In addition toeffects of gravity in promoting the separation of drill fluid/drillcuttings, the vibrating motion of the screen bed imparts mechanicalenergy to the drill cutting particles to “shake-loose” fluids that maybe adhered to the outer surfaces of the drill cuttings by surfacetension. Upon separation, drilling fluids will flow by gravity,atmospheric pressure, hydrostatic pressure of the fluid on the screen ora combination of all three through the screen where they are collected.As is known, this style of shaker and others are typically able toseparate drilling fluid from drill cuttings from an initial drillingfluids/cuttings value in excess of 100 wt % to a level of about 40-15 wt%.

As shown in FIGS. 2A-2B, and in accordance with the invention, theshaker is provided with a vacuum system 50 located below the screen bed12 to enhance the separation of drilling fluids from drill cuttings andthe flow of drilling fluid through the screen. As best shown in FIGS.1-1E and 6, a screen 7 is provided with at least one vacuum manifold 1,1 a, 1 a′ for applying a vacuum pressure to the underside of a portionof the screen 7 and shaker bed 12. That is, the vacuum manifold isdesigned to connect to the underside of a screen in order that ascuttings and fluids pass over the screen, a vacuum pressure gentlyencourages the passage of drilling fluid through the screen and/or toeffectively break the surface tension of fluids adhering to the drillcuttings and/or screen, hence improving the efficiency of separation andrealizing lower drilling fluid retained on cuttings levels. It is alsopreferred that the vacuum manifold is tapered and/or curved tofacilitate the flow of vacuumed materials away from the screen andotherwise over time, minimize the risk of solids collecting ordepositing within the system.

As shown in FIGS. 1-1 E and 2A-3B, the horizontal length of the vacuummanifold is designed to apply a vacuum across a relatively small area ofthe total area of the screen bed 12 and at the downstream end of thescreen. These figures show a vacuum area extending across the fullhorizontal width of the screen bed and in a typical shaker approximately7 inches of the total length of the screen bed 12. This amount ispreferably about 5-15% of the total length of the screen bed. In oneembodiment, the vacuum manifold extends up to 33% of the total length ofthe shaker screen, as shown by the dotted lines 22 in FIG. 5, whichrepresent a length that is 33% of the total length of the shaker screen.

The use of a relatively small area of the total screen bed area ispreferred in order to delineate between different separation mechanisms.That is, it is preferred that at the upstream end of the shaker,mechanical separation mechanisms are utilized to provide primaryseparation whereas at the downstream end the vacuum is applied toprovide secondary separation (in addition to shaking). This physicalseparation of the shaking and vacuum separation techniques maximizes theeffectiveness of both separation techniques without the detrimentaleffects of cuttings degradation and any downstream effects that cuttingsdegradation and/or passage through the screen would have on drillingfluid rheology such as plastic viscosity inter alia. As explained ingreater detail below, maintaining a film of drilling fluid prior tofinal vacuum treatment minimizes the abrasive and destructive effects ofdrill cuttings abrading one another.

Also as shown in FIG. 1 for example, although not essential, separatevacuum manifolds 1 a and 1 a′ are utilized across the width of thescreen to ensure that a relatively even and controllable amount ofvacuum pressure can be applied across the screen.

As shown in FIGS. 1B, 1E, 3A and 3C, seiving screen(s) 7 is/areoperatively attached to a vacuum frame and manifold 1 with a fluidconveyance tube/vacuum tube 3 to a vacuum system 50 with a vacuum gauge12 d and a fixed vacuum device 12 f (FIG. 3A) or variable vacuum device12 g (FIG. 3B). Both embodiments have a fluid separation and collectionsystem 13 that allows recovered drilling fluid to be separated from thevacuum system to a storage tank for re-use.

FIGS. 2A and 2B show a preferred embodiment of a fluid separation system13 having multi-stage fluid/solids separation. In this system, a primaryaccumulator tank 51 enables first-stage fluid/gas separation. Asecondary accumulator 52 in series with the primary accumulator providessecondary fluid/gas separation. Each stage includes appropriate fluidlevel detection systems and valves to ensure system shutdown in theevent that accumulated fluid levels become too high. The fluidseparation system 13 is configured to the vacuum frame and manifold 1and to a vacuum compressor 53. Drilling fluids may be recovered from thebottom of the accumulator tank 51 by port 54.

As shown in FIGS. 2A and 2B, the vacuum adjustment system can be arestrictive orifice 12 f or a controlled air/atmospheric leak into thevacuum line 12 g as known to those skilled in the art. A restrictiveorifice constricts flow and leads to a build up in the vacuum line,while a controlled atmospheric leak does not restrict flow. The vacuumgauge 12 d is useful for tuning but is not absolutely necessary.

Vacuum to Screen Interface and Screen Design

As shown in FIGS. 1-1E, at least one vacuum manifold 1 a, 1 a′, isadapted for configuration and sealing to a screen 7 by a vacuum manifoldsupport frame 6 (collectively vacuum frame and manifold 1). The vacuummanifold support frame 6 may include a bisecting bar 8 defining a vacuumarea 11 and open area 5. Each vacuum manifold 1 a, 1 a′ has a generallyfunnel-shaped design allowing fluids passing through the screen to bedirected to at least one vacuum hose connection 3. As shown in FIG. 1A,the upper edge of the vacuum manifold includes an appropriate connectionsystem and sealing system for attachment to the screen 7 such as amating lip 2 and sealing gasket 9. As shown schematically in FIG. 1A,the vacuum frame and manifold is installed above over support rails 20of the shaker basket and the screen 7 is connected to the upper side ofthe vacuum screen and manifold. A clamping system secures each of thesupport rails, vacuum screen and manifold and screen together. Theretro-fit assembly of the vacuum frame and manifold and screen to ashaker is best shown in FIGS. 4-6. FIG. 4 shows a plan view of a typicalshaker and shaker bed in which the shaking motors have been removed forclarity. The shaker bed includes a plurality of separate sections ofsupport members (20 a, b, c, d) onto which a screen 7 is normallymounted. The sections may be positioned at the same height or differentheights as known to those skilled in the art. Generally, if the sectionsare at different heights, one or more upstream sections may be higherthan one or more downstream sections.

As shown in FIGS. 1A and 5, the vacuum frame and manifold is placed ontop of the support members and a screen is placed on top such that thevacuum frame and manifold mates with the underside of the screen (FIGS.1A and 6). A clamping system such as pressure wedges secures the vacuumscreen and manifold and screen to the support members. Vacuum hoses areconnected to the manifold at ports 3 by an appropriate connection systemand run to the exterior of the shaker where they are connected to thevacuum and separation system 50.

In addition, the vacuum manifold and frame is provided with a seal 9around the four edges to ensure effective connection between the frameand manifold and prevent leakage of fluids. The seal 9 is preferably asolvent-resistant gasket such as Viton™ or nitrile rubber.

It is also preferred that a screen can be removed from the vacuum frame6 without requiring removal of the vacuum manifold and frame from thesupport rails 20.

EXAMPLES

A first trial of the system was made during a drilling operation atNabors 49, a drilling rig in the Rocky Mountains of Canada. The trialwas conducted while the rig was drilling and an oil-based invertemulsion drilling fluid was used. The well particulars and drillingfluid properties used during drilling are shown in Table 1 and arerepresentative of a typical well and drilling fluid.

TABLE 1 Drilling Fluid Properties Depth 4051 m T.V. Depth 3762 m Density1250 kg/m³ Gradient 12.3 kPa/m Hydrostatic 46132 kPa Funnel Viscosity 45s/l Plastic Viscosity 10 Mpa · s Yield Point 2 Pa Gel Strength 1/1.5 Pa10 s/10 min Oil/Water Ratio 90:10 HTHP 16 ml Cake 1 mm Chlorides 375714mg/l Sand Cont trace Solids Cont 12.88% High Density 402 kg/m³ (9.46 wt%) Low Density 89 kg/m³ (3.42%) Flowline 42° C. Excess Lime 22 kg/m³Water Activity 0.47 Electric Stability 396 volts Oil Density 820 kg/m³

The vacuum test was conducted on a MI-Swaco Mongoose Shaker.

For the first test, only one side of the vacuum system was connected sothat representative samples could be collected from both sides of thescreen to give a quantitative and qualitative assessment of the effectof vacuum on separation.

The vacuum system included a Westech S/N 176005 Model:Hibon vtb 820vacuum unit (max. 1400 CFM). The vacuum unit was pulling at 23 in. Hg.through a 22 inch×1 inch vacuum manifold during the test. An 84 meshscreen (i.e. open area of 50% such that the actual flow area through thescreen was 0.07625 ft²). During operation, the cuttings stream transitedthis vacuum gap in about 3 seconds.

Samples were collected during the test and there was a visibledifference between those processed over the vacuum bar and those whichpassed through the section without being subjected to a vacuum.

Qualitatively, the vacuum-processed cuttings were more granular anddryer (similar in consistency to semi-dry cement) whereas theun-processed cuttings (i.e. no vacuum) had a slurry-like texture typicalof high oil concentration cuttings.

The recovered test samples were then distilled (50 ml sample) using astandard oil field retort. The field retort analysis is summarized inTable 2.

TABLE 2 Trial Test Results-Field Retort Recovered Recovered Oil wt %/Oil vol %/ Sample Oil Water Oil Oil Oil Water wt % of vol % of Test (g)(ml) (ml) g/cc (g) % % Cuttings Cuttings Vacuum 90 14.5 2.0 0.82 11.9 8812 13.18 29.00 No 97 18.9 2.1 0.82 15.5 90 10 15.99 37.80 vacuum

Theseresults show a significant effect in about 3 seconds of exposure ofvacuum. In particular, test 1 showed that vacuum resulted in anapproximately 8 volume % improvement in oil recovery from the vacuumedcuttings.

During this trial, it was observed that excessive and/or an invariablevacuum pressure and airflow rate on the 1 inch screen could cause thevacuum screen to overcome screen vibration and to stall the cuttings onthe screen thereby preventing effective discharge of cuttings from theshaker. As a result, the vacuum system and screen design as shown inFIG. 5 where the vacuum is applied over approximately 7-10 inches(typically about 5-15% of the screen length) is preferred as greatercontrol on the vacuum pressure can be effected. Importantly, in order tominimize damage to the cuttings as they transition the screen, theposition of the vacuum should be such that the drilling fluid cushionbetween drill cuttings and the screen is minimal at the point that thecuttings engage the vacuum and that “dried” cuttings that do not havethe drilling fluid cushion do not engage with the screen for asignificant period of time so as to cause damage to the cuttings andcreate fines that may then transition the screen.

In addition, a pulsating or constant variable flow in vacuum pressuremay be utilized as a means of effectively stripping drilling fluid fromdrill cuttings. The operating frequency of such pulsations and/or thedegree of pulse pressure variation can be varied to prevent accumulatedfreezing of cuttings on the screen while also minimizing the time thatdry cuttings are in contact with the screen.

Further still, as is known, drilling fluids upon delivery to a shakerare often foamed as a result of dissolved gases within the drillingfluid expanding at surface which causes the drilling fluid to foam.

In the past, these foamed drilling fluids have decreased the performanceof the shaker that, depending on the severity of the foaming, mayrequire the addition of anti-foaming agents to enable effective drillingfluid separation using a shaker. in accordance with the invention, theuse of a vacuum not only de-foams the drilling fluid, it has beenobserved that a foamed drilling fluid subjected to vacuum will also haveimproved drilling fluid/drill cuttings separation wherein a foameddrilling fluid can result in a 1 wt % decrease in the drilling fluidsretained on cuttings value. As a result, in one embodiment, theinvention provides an effective method of de-foaming a drilling fluid asa result of the shaker/vacuum process. In addition, a drilling fluid mayalso be subjected to a pre-foaming treatment with a compressed gas inorder to improve the subsequent shaker/vacuum process. Pre-foaming canbe achieved in various ways including but not limited to positioning asparger 100 (with a gas injection system) in the fluid flow prior to thefluid passing over the shaker (FIG. 12). In addition, the action of thevacuum also provides a degassing capability that can act as an earlywarning system in the event that significant quantities of dangerousgases are contained in the drilling fluid. As explained in greaterdetail below, the use of one or more gas sensors 101 beneath the screenscan signal a significant quantity of gas which can be the trigger toutilize de-gassing equipment.

Cost Analysis

FIG. 7 shows an analysis of representative cost benefits realized by useof the separation system in accordance with the invention. As shown,drilling fluid volumes and drill cutting volumes are calculated based ona particular length of boreholes and borehole diameters.

FIG. 7 shows that over a representative 8 day drilling program, withonly a 3 wt % improvement in drilling fluid retained on cuttings, $7291in fluid costs would be saved based on the recovery of drilling fluidhaving a value of $900 per cubic meter.

As described below, these are conservative numbers as greater than 3 wt% improvements can be achieved and with drilling fluids of considerablyhigher value. For example, and in another scenario, if 2.4+cubic metresof drilling fluid per day is recovered from a typical installationhaving a fluid value of $1650/m³, the cost savings could be at least$4000/day.

In comparison to a prior art or conventional separation system wheresuch prior art cuttings processing equipment require mobilization anddemobilization costs as well as costing $1500-$2000 per day for rentalfees, conventional cuttings equipment is not cost effective as a meansof effectively reducing the overall costs of a drilling program.However, the system in accordance with the invention can be deployed ata significantly lower daily cost and hence allows the operator toachieve a net back savings on the fluid recovery.

Other Field Trials

Further field trials were conducted with results shown in Table 3.

TABLE 3 Field Trials with Varying Screen Sizes and Vacuum Rates VacuumVacuum Vacuum Screen Pump Manifold Flow Calculated Screen Open FlowDimensions Open Air Oil on Mesh Area Rate Width Length Vacuum AreaVelocity Cuttings Run (Mesh #) (%) (ft³/min) (in) (in) (in Hg) (ft²)(fpm) (% wt) Observations 1 84 49.80 1400 0.17 2 23 0.17 8434 7 Cuttings“frozen” 2 84 47.90 400 0.17 4 21 0.32 1253 8 Operational 3 84 49.80 4000.50 4 16 1.00 402 8.5 Operational 4 84 47.90 0 0.50 4 0 1.92 0 19 NoVacuum 5 84 49.80 400 0.50 4 7 1.99 201 9 Operational 6 105 46.90 4000.50 4 7 1.88 213 8 Operational 7 130 47.00 400 0.50 4 7 1.88 213 7.6Operational 8 145 46.40 400 0.50 4 7 1.86 216 7.2 Operational 9 13047.00 400 0.50 4 7 1.86 216 6.2 Operational 10 130 47.00 400 0.50 4 71.86 216 5.8 Operational 11 130 47.00 400 0.50 4 7 1.86 216 5.6Operational

The data presented shows the effect of different vacuum flow rates,manifold dimensions, vacuum gauge pressures, calculated air velocitiesand measured drilling fluids retained on cuttings values. The runsincluded screen mesh sizes of 84, 105, 130 or 145 mesh. In each case,the vacuum pump was operated at a flow rate of 400 cfm with theexception of Run 1 where a very high flow rate was used and Run 4 whichshows results when no vacuum was applied. For each run and for eachmanifold dimension, the observed vacuum gauge pressure was recorded andranged from 7 inches of Hg to 23 inches of Hg. The maximum gaugepressure that the vacuum pump was capable of pulling was 27 inches of Hgif the vacuum ports were completed closed off. Based on the manifoldsize and the vacuum pump flow rate, a calculated air velocity wasdetermined. Thus, the calculated air velocity for Run 1 where the openmanifold area was 0.17 ft² was approximately 8400 feet per minute.

Run 1 shows the results of a high calculated air velocity through thescreen. This flow rate resulted in the cuttings “freezing” on the screenthat then caused the cuttings to build up at that area. This requiredthat the shaker be stopped after a few minutes of operation to scrapeoff the vacuumed area of cuttings. The results show that this high airvelocity was effective in removing fluid from cuttings (i.e. 7 wt %fluid retained on cuttings) but from an operational perspective wasineffective due to the requirement to manually clear cuttings.

Runs 2 and 3 shows the effect of increasing the manifold area with acorresponding decrease in air velocity. In each of these cases, thesystem was operational in that cuttings did not freeze on the screen andthus permitted continuous operation.

Run 4 shows the baseline value of a shaker without the vacuum turned on.In this case, the drilling fluid retained on cuttings was 19 wt %.

Runs 5-11 show the effect of varying screen mesh size and the effect ondrilling fluid retained on cuttings. As shown, each of these runs wasoperational and resulted in substantially lower drilling fluid retainedon cuttings values. Importantly, it is noted that a finer screen (eg.130 mesh) showed drilling fluid retained on cuttings as low as 5.6 wt %.

From an operational perspective, with drilling fluid retained oncuttings values in the range of 5-9 wt %, the recovered cuttings had theappearance and consistency of semi-dry cement.

Table 4 shows further details of the properties of various samplesrecovered from the surface of a 130 mesh screen and the material balancefor use in calculating wt % and vol % of drilling fluid retained oncuttings values.

TABLE 4 Representative Values of Recovered Samples over 130 Mesh ScreenASG Solids Retort (50 mls) Oil (kg/m³) (after distillation) High DensityLow Density Oil on Screen Density (recovered Oil Water Solidsconcentration concentration Cuttings Mesh # (kg/m³) above screen) (mls)(mls) (mls) kg/m³ % kg/m³ % % wt % vol 130 818 2751 11.0 2.0 37.0 33.00.80 284.0 10.72 8.7 22.0 130 818 2751 8.5 2.0 39.5 33.0 0.80 284.010.72 6.3 17.0 130 818 2706 8.0 2.0 40.0 13.0 0.32 208.0 7.85 5.9 16.0130 818 2706 8.5 2.0 39.5 13.0 0.32 208.0 7.85 6.4 17.0 130 818 2662 7.52.0 40.5 2.0 0.05 149.0 5.62 5.6 15.0

As shown in FIGS. 8-11, a comparison between recovered drilling fluidsfrom different screen systems are shown. FIGS. 8 and 9 show the effectof an aggressive screen separation technique using a rotary vacuumdevice in accordance with the prior art. In a rotary vacuum device,cuttings enter a rotating screen tube to which a high vacuum pressure isapplied. Fluid is drawn off to the exterior of the tube as cuttingstumble over themselves during rotation of the tube. As shown in FIGS. 8and 9, the properties of the drilling fluid (at a given depth) usingrotary vacuum technologies are measured and graphed. The same propertieswere measured and graphed as shown in FIGS. 10 and 11 for a drillingfluid using screen vacuum technologies in accordance with the invention.As shown in FIGS. 8 and 9, rheological properties such as plasticviscosity (PV) and 10 minute gel strengths were significantly affectedover time as a result of the physical degradation of the drill cuttingsfrom the operation of the rotary vacuum machine where significantincreases in both these values were measured. In comparison, as shown inFIGS. 10 and 11, PV and 10 minute gel strengths values remained stablefor the subject technology. Emulsion stability was also favorable withthe vacuum screen as shown by an increasing emulsion stability for thevacuum screen technology.

Thus, the subject technology addresses one of the key problems with pastsystems where aggressive separation of drilling fluids results insignificant and detrimental effects on the drilling fluid rheology. Thatis, the subject technology preserves rheology and in particular plasticviscosity, 10 minute gel times and can improve emulsion stability, bysubstantially reducing fine solid concentrations in the recovered fluidsuch that the rheology of the recovered fluid is not significantlyaffected.

Further still, in order to the demonstrate the reduction in finesproduction, a post processing comparison of the drilling fluid recoveredby a rotary vacuum device and a vacuum screen device using a standardcentrifuge revealed that drilling fluid recovered from a vacuum screenhad a fraction (less than 10% of the volume) of the fines compared to arotary vacuum device.

Further still, the use of a vacuum screen in accordance with theinvention can also have a positive effect on fluid rheology by promotingthe oxidation of fatty acids in an oil-based drilling fluid which canimprove emulsifier usage in a well. With reference to FIG. 13, acomparison of primary and secondary emulsifier usage in wells thatutilized vacuum screen and roto-vac separation technologies is shown. Asshown, the vacuum screen required none or minimal additional emulsifiersto be added to the recovered drilling fluids during the course ofdrilling whereas the roto-vac well required additional emulsifiers. Inparticular, in cases where fatty acid emulsifiers can be oxidized, theuse of vacuum screens can assist in the oxidation of those fatty acidsby providing high air flow and drilling fluid mixing that promotes fattyacid oxidation. For example, the result of improved oxidation ofunsaturated fatty acid emulsifiers can be improved emulsificationproperties to the re-cycled drilling fluid after such drilling fluidsare re-introduced to the well. That is, as fatty acids are oxidized, theoxidation counteracts the potential detrimental effects of cuttings thuscontributing to a more consistent fluid viscosity that does not requirethe addition of further emulsifiers and thus improves the chemicalmaintenance costs of a drilling program.

Other Design and Operational Considerations

Adjustable Vacuum

It is understood that an operator may adjust the vacuum pressure, screensize and/or vacuum area in order to optimize drilling fluid separationfor a given field scenario.

Further still, in other embodiments the vacuum pressure and location canbe adjusted based on the relative area of the vacuum manifold withrespect to the underside of a screen. For example, a vacuum manifold maybe provided with overlapping plates that would allow an operator toeffectively widen or narrow the width of the manifold such that the openarea of the manifold could be varied during operation through anappropriate adjustment system so as to enable the operator to optimizethe cutting/fluid separation and, in particular, the time that thecuttings are exposed to a vacuum pressure.

Screen Cleaning

Another noted advantage of the system is the decreased requirement forscreen cleaning. As is known in the field, un-modified shaker systemsrequire that a screen, and in particular the downstream areas of ascreen, be cleaned periodically due to screen clogging. In comparison,because of the vacuum system, screen cleaning is not required as oftenwhich in the case of hydrocarbon based fluids will minimize the healthrisks of damaging mists being inhaled by the person performing thistask.

Screen Size Selection

Ultimately, the selection of screen size will be made predominantly onthe basis of drilling fluid viscosity wherein an operator may choose afiner screen for lower viscosity fluids and a coarser screen for higherviscosity fluids. However, the operator will generally choose the finestscreen for a given viscosity of drilling fluid that will provide adesired or optimal fluid retained on cuttings value.

Screen Design

Further, in that shaker baskets tend not to be all of an equal size evenwithin specific models of shakers, various modifications can be made thedesign of the screen to ensure that cuttings do not work their waybetween gaps that may exist within the equipment. For example, a gap canoften exist between the edge of the screen and the shaker basket suchthat cuttings/drilling fluid transit this gap and work their way betweenthe screen and the vacuum manifold; even with a gasket installed. Thus,in various deployments and/or different model shakers, improved sealingsystems may be required such as a raised-lip up from the manifold intothe screen body to improve the seal and/or the addition of gasketmaterial to the side of the screen between the screen side and thebasket to prevent solids from falling into the lower tray area.

Gas Detector

It is also preferred to include a gas detector 101 in the receiving areaof the vacuum and/or beneath the screen to detect buildup of harmfulgases within the chamber. The gas detector can be used as a warningsystem for an operator utilize degassing equipment.

Original Equipment

The embodiments described above have emphasized the ability to retro-fitthe vacuum system to various designs of known shakers. However, thevacuum design may also be incorporated into new shaker designs as wouldbe known to those skilled in the art. It is also understood that theability to retro-fit the design to various existing designs of shakersmay be limited by space limitations at the preferred downstream end ofthe shaker. However, many of the above described benefits can berealized with the vacuum system located at another region of the shakerincluding middle regions of the shaker bed.

Further still, other designs in the connection system between the vacuummanifold and screen beds can be implemented depending on the specificdesign of the shaker. For example, shakers having tensioned screens willutilize a different connection and sealing system to provide aneffective connection to the underside of a screen.

Installation

It is also beneficial to install the vacuum system at a level below theheight of the shaker to allow for collected fluid to flow as well as bedrawn into the vacuum chamber. This would ensure that slow movingdetritus/fluid would have less opportunity to collect in the hose systemthat exists between the vacuum system and the operative connectionbetween the screen and vacuum.

Accelerometer/Strain Gauges

In another embodiment, the shaker is provided with one or moreaccelerometer and/or strain gauges operatively connected to one or morelocations on the shaker. The gauges are configured to indirectly measurethe relative mass of the combined drilling fluid and cuttings on theshaker so as to provide a qualitative and/or quantitative assessment ofthe mass of fluid/cuttings on the shaker at different locations. Thatis, by determining the mass of fluid/cuttings at one position andcomparing it to the mass of fluid/cuttings at a different position, therelative degree of drilling fluids/cuttings separation may bedetermined. This data can be effective in controlling the operation ofthe shaker and/or vacuum system.

Composite Materials

In yet another aspect, the shaker may be constructed out of light weightmaterials such as composite materials as opposed to the steel currentlyused. The use of composite materials such as fiberglass, Kevlar and/orcarbon fiber may provide a lower reciprocating mass of the shaker system(including the screen frame, and associated shaking members), allow forhigher vibration frequencies to be employed by minimizing the momentumof the shaker and allow for more control of the amplitude of the shaker.That is, a composite design allows for higher vibrational frequencies tobe transmitted to the drill cuttings and fluid that would result in areduction of viscosity of the drilling fluids which are typicallythixotropic in nature. The resulting decrease in viscosity would providea greater degree of separation of fluid and cutting.

Still further, a composite shaker would be light enough to allow forstrain gauge sensors and accelerometers to be located under the shakebasket in order to track the flow of mass over the shaker in a way whichwould allow for the operator to know the relative amount of drillingdetritus being discharged from the well on a continuous basis. Thisinformation in combination with the known drilling rate and hole sizecan be used for adjusting fluid properties; typically viscosity, tooptimize the removal of cuttings from the well bore during theexcavation process.

Although the present invention has been described and illustrated withrespect to preferred embodiments and preferred uses thereof, it is notto be so limited since modifications and changes can be made thereinwhich are within the full, intended scope of the invention.

The invention claimed is:
 1. A method of optimizing the performance of adrill cuttings shaker comprising the steps of: a. introducing drillcuttings contaminated with drilling fluid to an upstream end of a shakerbed supporting a shaker screen; and b. applying a vacuum force to theshaker screen or a section of the shaker screen sufficient toeffectively reduce drilling fluid retained on cuttings to a level belowthat obtained when no vacuum force is applied; wherein the vacuum forceis applied to at least 5% and less than 33% of the length of the shakerscreen adjacent to a downstream end of the shaker screen, and wherein aremaining portion of the shaker screen has no vacuum force applied. 2.The method as in claim 1 wherein the drilling fluids retained oncuttings after step b is less than 12 wt %.
 3. The method as in claim 1wherein the drilling fluids retained on cuttings after step b is lessthan 10 wt %.
 4. The method as in claim 1 wherein the drilling fluidsretained on cuttings after step b is less than 8 wt %.
 5. The method asin claim 1 wherein the drilling fluids retained on cuttings after step bis less than 6 wt %.
 6. The method as in claim 1 wherein the vacuumforce is applied across 5-15% of the length of the shaker screen.
 7. Themethod as in claim 1 wherein the vacuum system provides an air flowthrough the screen of 201-8400 feet per minute.
 8. The method as inclaim 1 wherein the vacuum system is controlled to provide an air flowthrough the screen to cause defoaming of a drilling fluid.
 9. The methodas in claim 1 where the drilling fluid is foamed prior to contacting theshaker screen.
 10. The method as in claim 1 wherein the vacuum system iscontrolled to provide an air flow through the screen to effect fattyacid oxidation within the drilling fluid.
 11. An apparatus for improvinga separation of drilling fluid from drill cuttings on a shaker, theapparatus comprising: a shaker screen having an upper side and a lowerside for supporting drilling fluid contaminated drill cuttings within ashaker; an air vacuum system operatively connected to a section of theshaker screen for pulling an effective volume of air through the sectionof the shaker screen to enhance a flow of drilling fluid through thesection of the shaker screen and the separation of drilling fluid fromdrill cuttings; and, a drilling fluid collection system for collectingthe separated drilling fluid from an underside of the shaker screen andthe air vacuum system; wherein the air vacuum system has a vacuumcontrol system operable to control a volume of air through the sectionof the shaker screen to minimize damage to the drill cuttings whileenhancing an amount of drilling fluid removed from the drill cuttingsand maintaining an effective flow of drill cuttings off the shaker;wherein the air vacuum system includes a vacuum manifold operativelyconnected to a section of the shaker screen and extending at least 5%and less than 33% of the total length of the shaker screen adjacent to adownstream end of the shaker screen, and wherein a remaining portion ofthe shaker screen has no air vacuum system.
 12. The apparatus as inclaim 11 wherein the air vacuum system includes: a vacuum hoseoperatively connected to the vacuum manifold and a vacuum pumpoperatively connected to the vacuum hose.
 13. The apparatus as in claim12 further comprising a fluid/gas separation system operativelyconnected to the vacuum pump.
 14. The apparatus as claim 13 wherein thefluid/gas separation system is a multi-stage fluid separation system.15. The apparatus as in claim 12 wherein the vacuum manifold has afunnel shaped portion for operative connection to the vacuum hose. 16.The apparatus as in claim 12 wherein the vacuum manifold extends up to15% of the total length of the shaker screen towards the upstream end ofthe shaker screen.
 17. The apparatus as in claim 11 wherein a vacuumsystem applies a pulsating vacuum pressure.
 18. The apparatus as inclaim 11 wherein the vacuum manifold is adapted for configuration to theshaker screen across 5-15% of the length of the shaker screen.
 19. Theapparatus as in claim 11 wherein the shaker screen includes a shakerframe and the shaker frame and associated shaking members aremanufactured from composite materials.
 20. The apparatus as in claim 11wherein the shaker screen is 50-325 mesh or a combination thereof. 21.The apparatus as claim 11 wherein the shaker screen is 80-150 mesh or acombination thereof.
 22. The apparatus as claim 11 wherein the vacuumsystem is operable to pull air through the shaker screen at a velocityof 201-8400 feet per minute.
 23. The apparatus as in claim 11 whereinthe manifold includes a lip supporting a gasket and the screenoperatively engages with the gasket and the lip.
 24. The apparatus as inclaim 11 wherein the vacuum system is operable to produce drillingfluids retained on cuttings of less than 12 wt %.
 25. The apparatus asin claim 11 wherein the vacuum system is operable to produce drillingfluids retained on cuttings of less than 10 wt %.
 26. The apparatus asin claim 11 wherein the vacuum system is operable to produce drillingfluids retained on cuttings of less than 8 wt %.
 27. The apparatus as inclaim 11 wherein the vacuum system is operable to produce drillingfluids retained on cuttings of less than 6 wt %.
 28. The apparatus as inclaim 11 further comprising an air injection device for operativeinjection of a compressed gas into the drilling fluid for foaming thedrilling fluid prior to the drilling fluid contacting the shaker screen.29. An apparatus for improving the separation of drilling fluids fromdrill cuttings on a shaker, the apparatus comprising: a shaker screenhaving an upper side and a lower side for supporting drilling fluidcontaminated drill cuttings within a shaker; an air/liquid vacuum systemoperatively connected to the shaker screen, the air/liquid vacuum systemfor drawing air and drilling fluid through the shaker screen, theair/liquid vacuum system including: an air vacuum pump; a manifoldoperatively connected to a section of the shaker screen and extending atleast 5% and less than 33% of the length of the shaker screen forcollecting drilling fluid from an underside of the shaker screen; aseparate gas/liquid separation system operatively connected to the airvacuum pump between the air vacuum pump and the manifold, the gas/liquidseparation system having a closed fluid collection system for collectingrecovered drilling fluid; and a vacuum adjustment system operativelyconnected to the air/liquid vacuum system between the gas/liquidseparation system and the shaker screen for tuning a flow of gas/liquidbetween the gas/liquid separation system and for controlling a volume ofair through the shaker screen; wherein the air vacuum pump is connectedto the gas/liquid separation system for conveying a gas/liquid mixturefrom the manifold to the gas/liquid separation system and air from thegas/liquid separation system; wherein the manifold is connected to theshaker screen adjacent to a downstream end of the shaker screen only andwherein a remaining portion of the shaker screen has no air vacuumsystem.
 30. The apparatus as in claim 29 wherein the manifold has amating lip having a lower surface for engagement with support rails ofthe shaker, and an upper surface for supporting the shaker screen.